https://www.amazon.com/Never-Split-Difference-Negotiating-De...
https://www.amazon.com/Effective-Negotiating-Strategies-Succ...
https://www.amazon.com/Pre-Suasion-Revolutionary-Way-Influen...
[0]: https://www.kalzumeus.com/2012/01/23/salary-negotiation/
His company website is http://www.tableforce.com/ you can grab some free material from there.
Even if you just took away the points on mirroring and asking calibrated questions, you would be far ahead from where you are now.